In recent years there has been an explosive growth in the use of glass as cover lens for consumer electronic devices with displays, such as mobile phones, tablets, and laptop computers. Part of the reason for this explosion is due to increased resistance of glass cover lenses to damage as a result of improvements in glass manufacturing processes and compositions. Glass cover lenses also improve the tactile feel of touch display operation while enhancing the aesthetic appeal of the devices.
Glass cover lenses typically have decorations printed on them for various reasons. One use of decorations is to mask the electronic components in the interior of the device from the view of the user. Another use of decorations is as logos that distinguish one product or brand from another. Decorations may also function as icons that indicate the status of the device or location for touch buttons. Decorations may also be used to simply enhance the aesthetic appeal of the device.
Decorations are typically in the form of ink coatings on the surfaces of the cover lenses. To be suitable for the uses mentioned above, the ink coating should have sufficient optical density to effectively block light and have no visible defects such as pinholes and saw edges. The ink coating should maintain adhesion and color under all environments where the device is expected to operate. The coating should also be compatible with other functions of the device, such as being thin enough not to interfere with assembly of the cover lens to the touch display module of the device and having high enough electrical resistance not to interfere with the function of the wireless antennae of the device.
The current state of the art is to print decorations on glass cover lenses using screen printing. For repeatedly printing the same design on a large number of cover lenses, screen printing is a mature process with relatively fast cycle time and low cost. However, there are some challenges with screen printing. The screen printing process is constantly changing due to evaporation of solvents in the ink during printing, wear in the screen emulsion and squeegee, and loss of tension in the screen. Any environmental contamination of the screen during printing would prevent ink from being deposited onto the substrate in the contaminated areas, causing pinhole defects. These pinholes can be reworked by manually applying ink at the defect location or by printing an additional layer of the same ink over the existing ink layer to cover the defects or by stripping all the ink from the glass part and reprinting. Each of the rework methods increases cost of fabrication and risk of other defects being introduced during the additional processing.
The screen printing process is also limited in the type of patterns that can be fabricated. When applying multiple colors on the cover lens, each color has to be printed in a separate layer, with each layer being cured in between applications. The multiple steps greatly lengthen the overall processing time, increase cost of fabrication with each additional layer printer, as well as increase the rate of yield loss due to extra processing. These challenges restrict the options available to device designers for design of the cover lens. To date, device cover lenses typically have no more than six different colors, and usually only two to four different colors. Each new color used in the decorative design requires a new ink. The required customization slows the response time from new design orders to finishing of cover lenses. Accordingly, there is a need for a method of applying decorations having a plurality of patterns and/or colors, without the drawbacks of traditional printing methods, such as screen printing.